Metadata Write Back

[jeg]

When writing metadata I noticed that the whole thing goes very slowly. As shown in the screenshot, there are many instances of exiftools but only one or two are used. Not more than 5 images per minute are written. The images are JPG and RAW files (XMP).

[Mario]

Please at least include a log file in debug mode when you are reporting issues.
This gives us a minimum information to work with.

Also include mandatory data, e.g. which file formats you are using, if the images are on a local SSD (good) or remove NAS box (not so good, performance wise).
A screen shot of Windows Task Manager does not help much. The number of processes IMatch uses depends on the core count and user settings.

IMatch uses far more ExifTool instances for reading than for writing, for example.
And the number of processes is even user configurable under Edit > Preferences > Application. Did you make changes there?

The log file (in Debug mode, see link above) will show us which files IMatch is writing, how long it takes exactly to write the file and to read back the updated metadata etc.